Search for Axionlike and Scalar Particles with the NA64 Experiment

Photoproduction of axionlike particles in the NA64 experiment

“…The additional inefficiency of the detector due to instrumental effects not included in the MC-simulation is assumed to be negligible. It was below 20% in the published result [37] and will be significantly decreased after the detector upgrade in 2020-2021.…”

“…The background in the visible signature is caused mainly by the punchthrough leading K 0 and neutrons produced in electronuclear interactions in ECAL [37]. The background in both signatures is shown to be smaller than 0.2 events [16,37], so that it can be neglected in the sensitivity estimates since the difference from the background free case is small. After the upgrade of the NA64 detector in 2020-2021 it will be further suppressed.…”

Search for Axionlike Particles Produced in e+e− Collisions at Belle II

“…This work was supported by the following funding sources: L. ) on the ALP-photon coupling from this analysis and previous constraints from electron beamdump experiments and e þ e − → γ þ invisible [6,9], proton beamdump experiments [8], e þ e − → γγ [11], a photon-beam experiment [12], and heavy-ion collisions [13].…”

“…In the MeV=c 2 to GeV=c 2 mass range, the current best limits for ALPs with photon couplings are derived from a variety of experiments. These limits come from e þ e − → γ þ invisible and beam-dump experiments for light ALPs [6,8,9], from e þ e − → γγ [10,11] and coherent Primakoff production off a nuclear target [12] for intermediate-mass ALPs, and from peripheral heavy-ion collisions [13] for heavy ALPs.…”

Invisible decays of axion-like particles: constraints and prospects

“…Our aim is to capture the general phenomenological aspects of an ALP with independent couplings to electron and photons, studying correlations between processes induced by the different interactions, with particular attention to possible changes in the existing limits. We cover all available missing-energy searches, including high-energy results from the DELPHI [40] as well as high-intensity frontier experiments as BaBar [41] and NA64 [42], and we also present projections for Belle-II [43]. As an illustration of the effect of adding an invisible decay channel for standard long-lived ALP beam dump searches, we further study the limit from the E137 experiment [44] as function of the ALP invisible JHEP06(2021)009 branching ratio.…”